a) Field of the Invention
This invention relates to a syringe, and more specifically to a syringe with a Luer-Lok portion for connecting an extension tube, a three-way cock or a disposable needle.
b) Description of the Related Art
To mix a solution of a medicine in a transfusion or the like or to inject a high-viscosity medicine or the like into the body, a plastic-made syringe with a Luer-Lok portion for connecting an extension tube, a three-way tube or a disposable needle to a free end portion (air nozzle) of the syringe has been used.
A conventional syringe having a Luer-Lok portion will be described with reference to FIG. 1A through FIG. 4B, in which:
FIG. 1A is a perspective view of the conventional syringe having the Luer-Lok portion;
FIG. 1B is an enlarged perspective view of a conical-frustum-shaped free end portion of the conventional syringe without the Luer-Lok portion;
FIG. 2 is a schematic cross-sectional view of the Luer-Lok portion of the conventional syringe;
FIG. 3 is a perspective view of a cylindrical connector to be screwed in the Luer-Lok portion of the conventional syringe;
FIG. 4A is a simplified cross-sectional view illustrating a normal state of connection between the connector and the Luer-Lok portion; and
FIG. 4B is a simplified cross-sectional view depicting a state of connection between the connector and the Luer-Lok portion, in which the connector has been excessively screwed in the Luer-Lok portion.
The Luer-Lok portion, which is designated at numeral 1, has a double-cylinder structure composed of an outer cylindrical portion 2 and an inner cylindrical portion (Luer nozzle) 3, which are both arranged upright on a plane 4 of truncation of the conical-frustum-shaped free end portion of the syringe. The plane 4 of truncation is shown as a top flat surface in FIG. 1B. Between both the cylindrical portions, the cylindrical connector 8 shown in FIG. 3 is screwed in to bring them into engagement with each other. Although not shown in FIG. 3, the cylindrical connector 8 is arranged at an end portion of an extension tube or the like to be connected to the Luer-Lok portion 1.
Reference is next had to FIG. 2. Formed on an inner peripheral surface 2' of the outer cylindrical portion 2 of the Luer-Lok portion 1 are two projecting helical ribs (hereinafter simply referred to as "projecting ribs" for the sake of brevity) a,b, which are parallel to each other and are adapted to connect to the Luer-Lok portion 1 the connector 8 (see FIG. 3) arranged at the end portion of the extension tube or the like. These projecting ribs a,b consist of mutually-parallel two projecting ribs, which helically extend downward at the same pitch on the inner peripheral surface 2' of the outer cylindrical portion 2 with the positions of their upper ends being shifted, for example, over about 180 degrees from each other.
To connect the connector 8 (see FIG. 3) to the Luer-Lok portion 1, the connector 8 for the extension tube or the like, said connector 8 being provided on an outer peripheral surface thereof with mutually-parallel two projecting ribs a',b' formed likewise as the projecting ribs a,b, is screwed in along grooves defined between the projecting ribs a,b so that the connector 8 and the Luer-Lok portion 1 are brought into engagement with each other.
The mutually-parallel two projecting ribs a,b in the Luer-Lok portion 1 have such a pitch that they substantially circle once on the inner peripheral surface 2' of the outer cylindrical portion 2. The grooves defined between the projecting ribs a,b are formed so that they have a constant width and their respective lower end portions generally extends to an upper surface 5 of a bottom wall between the outer cylindrical portion 2 and the inner cylindrical portion 3. Further, the angles formed between the projecting ribs a,b and a horizontal plane are acute. By the way, the term "the thickness (t.sub.1) of the bottom wall" (see FIG. 2) as used herein means a distance between the plane 4 of truncation of the conical-frustum-shaped free end portion and the upper surface 5 of the bottom wall.
Incidentally, the height (H) of the inner cylindrical portion 3 from the upper surface 5 (reference plane) of the bottom wall between the outer and inner cylindrical portions (hereinafter called "both the cylindrical portions") 2,3, the inner diameter (d.sub.1) of the outer cylindrical portion 2, the degree of tapering of an outer surface of the inner cylindrical portion 3, the difference (.DELTA.H) between both the cylindrical portions, and the like have been specified by the ISO (International Organization for Standardization). Data of the respective portions in the conventional art are, for example, as follows: thickness (t.sub.1) of the bottom wall: about 1 mm or so, H: 9.20 mm, .DELTA.H: 2.1 mm, the degree of tapering: 6/100, and d.sub.1 : 7.80 mm.
Since the Luer-Lok portion 1 of the syringe according to the above-described conventional art is constructed as described above, excessive screwing of the connector 8 for the extension tube or the like in the Luer-Lok portion 1 in an attempt to make a free end portion of the connector 8 extend to the upper surface 5 of the bottom wall of the Luer-Lok portion 1 for the achievement of complete connection of the connector 8 upon connecting the connector 8 to the Luer-Lok portion 1 tends to cause bending of the free end portion of the connector 8 as shown in FIG. 4B so that the outer cylindrical portion 2 is pushed outwards. As a result, a stress is concentrated at a root portion of the outer cylindrical portion 2, leading frequently to breakage of the outer cylindrical portion 2 around the root portion. Through the root portion, the outer cylindrical portion is connected to the plane 4 of truncation of the conical-frustum-shaped free end portion. With a view to avoiding such breakage, various attempts have been made including making the thickness of a boundary area between a lower end portion of the outer cylindrical portion 2 of the Luer-Lok portion 1 and the plane 4 of truncation of the conical-frustum-shaped free end portion greater than that in the conventional art. Such attempts are however still insufficient to protect the Luer-Lok portion 1 from breakage. There is accordingly a desire for improvements.